Pressure resistant heat-sensitive copying sheets



Feb. 22, 1966 P. ADHIKARY 33369717 PRESSURE RESISTANT HEAT-'SENSITIVE COPYING SHEETS Filed Nov. 29. 1961 OPAQUE COATING TRANSPARENT TISSUE PAPER LOPAQUE DARK PAPE R FIG2 TRANSPARENT TISSUE PAPER OPAQUE COATING LOPAQUE DARK PAPER United States Patent O 3,236,717 PRESSURE RESISTANT HEAT-SENSITIVE COPYING SHEETS Pashu Adhikary, Nyack, N.Y., assignor to Interchemical Corporation, New York, N.Y., a corporation of Ohio Filed Nov. 29, 1961, Ser. No. 155,848 7 Claims. (Cl. ll- 6) This invention relates to heat-sensitive copying sheets useful in preparing copies of printed matter or other graphic originals.

Heat-sensitive copying sheets are old in the art. In fact, there are at least two distinct types of such sheets. One operates by means of a heat activated chemical change that occurs in the sheet, or in the coating on the sheet. Another type operates by means of a physical change that is produced by heat. In the latter type, the image formation may result from the transparentization of an opaque coating comprising a fusible composition as in U.S. Patent No. 2,710,263 and Reissue Patent No. 24,554 or from the transparentization of a blushed lacquer coating as in copending application S.N. 840,523 and continuation-in-part No. 150,134 of said application Iiled -on or about November 6, 1961, to show a dark background or a background of contrasting color.

While said heat-sensitive sheet which operates by means of a physical change has been extensively used, such use has been hampered because said paper has a pressure sensitivity which is less than desirable.

I have now discovered a novel `heat-sensitive copying sheet which operates by means of a physical change but which has greatly diminished pressure sensitivity.

My novel heat-sensitive .sheet comprises a base sheet, preferably of a dark color, carrying ya coating of contrasting color which is adapted on being placed in heat-conductive relationship with a graphic original having graphic representations highly absorbtive of infra-red rays and upon irradiation of said graphic original with infra-red rays to transparentize in the area proximate to said graphic representations to produce a copy of said graphic original, said coating having imbedded therein a transparent porous fibrous sheet.

Preferably the transparent sheet is a transparent tissue paper. Such a paper must have a porosity suiiicient to render said paper transparent. For example, a suitable degree of transparency may be defined by the ability of the transparent sheet to transmit a readable image of ordinary printed matter illuminated by a 60 Watt light bulb at a `distance of 18 inches when said sheet is maintained at a distance greater than 1A6 inch from said printed matter. Advantageously, the porosity is the minimum porosity which will result in a transparent sheet. As the porosity is increased from this minimum, the pressure sensitivity of the sheet also increases. However, there is no critical maximum porosity, since even a heat-sensitive sheet containing a tissue of very great porosity would still display less pressure sensitivity th-an would the same heat-sensitive sheet without the incorporated tissue.

While it is preferred to use tissues paper as the transparent sheet, transparent porous brous sheets of other materials may be readily used. The `sheets may be made of other natural bers such as silk or cotton or synthetic fibers such as cellulose acetate, viscose rayon, nylon, acrylic iiber such as Orlon and polyester ber such as Dacron Transparent fibrous sheet may be woven, e.g., a silk screen but it is preferable that the sheet be non-woven such as tissue paper, the preferred embodiment.

While the illustrative examples show the copying sheet employing a blushed lacquer coating as described in co- ICC pending application S.N. 840,523 and the continuation-inpart thereof, the novel copying sheet of this invention may also employ the coatings set forth in U.S. Patent No. 2,710,263 and Reissue Patent No. 24,554 which comprise compositions consisting of particles of a normally transparent stable organic fusible solid, melting Within the range of 60-115" C., dispersed in a solution of a transparent lm-forming binder in a volatile solvent. After the applications of the coating, the solvent is evaporated without fusing or dissolving the particles so as to provide a non-transparent, infra-red transmitting, heat-sensitive layer.

As set forth in copending application S.N. 840,523 and its continuation-in-part, the blushed lacquer `coatings may be produced by dissolving a film-forming material such as nitrocellulose, ethyl cellulose, cellulose acetate and vinyl resin, with or without plasticizer, colorants, or other additives, in a mixture of volatile liquids of different boiling point and evaporation rate; the liquid with the fastest evaporation rate being a solvent for the film-former while the slower evaporating liquid is a non-solvent for the film-former. Thus when the blushing lacquer is applied to a substrate and the volatile liquids are allowed to evaporate the liquid mixture becomes less and less a solvent for the film-former as the more volatile solvent evaporates. The film-former precipitates from such a system as an opaque, or blushed iilm.

In this description and claims, all proportions are by weight unless otherwise stated.

In making the heat-.sensitive copying sheet of this invention, the transparent porous librous sheet may be superimposed upon a preferably `dark colored surface of a base sheet and the coating composition applied to exposed surface of said transparent sheet and, then, said coating permitted to dry. Alternatively, the coating composition may be applied first to said base sheet and, before the coating dries, the transparent sheet is placed upon said wet coating and sinks into said coating.

It is preferred that the base sheet, coating composition and transparent sheet be transparent to infra-red radiation :since infr-a-red is the most effective radiation for use in thermocopying. Where the heat-sensitive sheet is to be used for front copying, it is, of course, essential that the sheet be substantially transparent to the radiation used to develop the copies. If the heat-sensitive sheet is to be used only for back copying, said sheet need not be transparent to infra-red because the radiation does not pass through the sheet.

The following examples will further illustrate the practice of this invention.

Example 1 A 51/2 lbs. transparent white tissue paper is superimposed upon a 41/2 lbs. blue opaque paper of the type conventionally used in making carbon paper. Both of said papers are infra-red transmitting. A composition consisting of 4 parts cellulose acetate butyr-ate, 4 parts of tricresyl phosphate, 10 parts of naphthol mineral spirits (boiling range 310-338 C. and K.B. value 34.0) and 2-8 parts of methyl ethyl ketone is uniformly applied to the exposed surface of said white tissue in a conventional manner, eg., using a M-ayer Coater at room temperature. The solvents are then permitted to evaporate at room temperature to produce a uniform blush coating, having said white tissue imbedded therein, upon said blue paper base. The coating Weight is about 2.7 mg. per square inch. The coating displays good adhesion and excellent abrasion and pressure resistance. The resulting heat-sensitive copying sheet can be used to produce copies by the front or back printing techniques using the Thermo- Fax copying machine. A diagrammatic section of the sheet of this example appears as FIG. l in the drawings.

3 Example 2 Example l is repeated using the same ingredients, conditions and procedure except that the coating composition is applied direct to the blue base sheet before the transparent tissue paper is superimposed and then the tissue paper is superimposed onto the coating while the coating is still wet (before the solvent has evaporated). The tissue sinks into the coating and the latter dries to a uniform film. The resulting sheet has the same properties as those of the sheet described in Example l. A diagrammatic section of the sheet of Example 2 appears as FIG. 2 in the drawings.

Example 3 Example 1 is repeated using the same conditions except that instead of the composition of Example 1, the following composition is used:

Vinyl chloride-vinyl acetate copolymer (8S-88% chloride and mol. wt. of about 10,000) 12.8 Methyl ethyl ketone 38.5 Butanol 33.3 Butyl stearate 15.4

The resulting heat-sensitive copying sheet has the same properties as those described in Example 1.

Example 4 Example l is repeated using the same conditions except that instead of the composition of Example 1, the

The resulting heat-sensitive copying sheet has the same properties as those described in Example 1.

While there have been described what are, at present, considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, intended to cover all such changes and modifications `as fall within the true spirit and scope of the invention.

What is claimed is:

1. A heat-sensitive copying sheet adapted, on being placed in heat-conductive relationship with `a graphic original having graphic representation highly absorbtive of infra-red rays and on irradiation of said graphic original with infra-red rays, to undergo a physical change to produce a copy of said graphic original, said copying sheet comprising a base sheet having a normally opaque heat transparentizable coating thereon of contrasting color and said coating enclosing `and covering a transparent porous fibrous sheet the porosity of the sheet being such that the sheet has a degree of transparency defined by the ability of the s'heet to transmit a readable image of ordinary printed matter illuminated by a watt light bulb at a distance of 18 inches from the printed matter when said sheet is maintained at a distance greater than /l; inch from said printed matter.

2. The copying sheet defined in claim 1 wherein said enclosed fibrous sheet is a transparent paper.

3. The copying sheet defined in claim 2 wherein said enclosed fibrous sheet is tissue paper.

4. A heat-sensitive copying sheet adapted, on being placed in heat conductive relationship with a graphic original having graphic representative highly absorbtive of infra-red rays and on irradiation of said graphic original with infra-red rays, to produce a copy of said graphic original, said copying sheet comprising a base sheet having -a heat transparentizable blushed lacquer coating thereon of contrasting color and said coating enclosing and covering a sheet of transparent tissue paper the porosity of the sheet being such that the sheet has a degree of transparency defined by the ability of the sheet to transmit a readable image of ordinary printed matter illuminated by a 60 watt light bulb at a distance of 18 inches from the printed matter when said sheet is maintained at a distance greater than 1/16 inch from said printed matter.

5. A heat-sensitive copying sheet adapted, on being placed in heat-conductive relationship with a graphic original having graphic representations highly absorbtive of infra-red rays and on irradiation of said graphic original with infra-red rays, to undergo a physical change to produce a copy of said graphic original, said copying sheet comprising a base sheet having a normally opaque heat transparentizable coating thereon of contrasting color and said coating carrying an upper transparent porous fibrous sheet the porosity of the sheet being such that the sheet has a deg-ree of transparency defined by the ability of the sheet to transmit a readable image of ordinary printed matter lilluminated by a 60 watt light bulb at a distance of 18 inches from the printed matter when said sheet is maintained at a distance of greater than 1/16 inch from said printed matter.

6. The copying sheet defined in claim 5 wherein said upper fibrous sheet is a transparent, porous paper.

7. The copying sheet defined in claim 6 wherein said upper fibrous s'heet is tissue paper.

References Cited by the Examiner UNITED STATES PATENTS 2,605,205 7/1952 Patterson et al 154-43 2,710,263' 6/ 1955 Clark 117-36.7 `2,927,039 3/ 1960 Vander Weel ll7-36.7 3,076,721 2/1963' Coles et al 117-369 ALEXANDER WYMAN, Primary Examiner.

EARL M. BERGERT, Examiner. 

4. A HEAT-SENSITIVE COPYING SHEET ADAPTED, ON BEING PLACED IN HEAT CONDUCTIVE RELATIONSHIP WITH A GRAPHIC ORIGINAL HAVING GRAPHIC REPRESENTATIVE HIGHLY ABSORBTIVE OF INFRA-RED RAYS AND ON IRRADIATION OF SAID GRAPHIC ORIGINAL WITH INFRA-RED RAYS, TO PRODUCE A COPY OF SAID GRAPHIC ORIGINAL, SAID COPYING SHEET COMPRISING A BASE SHEET HAVING A HEAT TRANSPARENTIZABLE BLUSHED LACQUER COATING THEREON OF CONTRASTING COLOR AND SAID COATING ENCLOSING AND COVERING A SHEET OF TRANSPARENT TISSUE PAPER THE POROSITY OF THE SHEET BEING SUCH THAT THE SHEET HAS A DEGREE OF TRANSPARENCY DEFINED BY THE ABILITY OF THE SHEET TO TRANSMIT A READABLE IMAGE OF ORDINARY PRINTED MATTER ILLUMINATED BY A 60 WATT LIGHT BULB AT A DISTANCE OF 18 INCHES FROM THE PRINTED MATTER WHEN SAID SHEET IS MAINTAINED AT A DISTANCE GREATER THAN 1/16 INCH FROM SAID PRINTED MATTER. 